Effect of rumen-protected choline on dairy cow metabolism, immunity, lactation performance, and vaginal discharge microbiome.

Rumen-protected choline (RPC) promotes benefits in milk production, immunity, and health in dairy cows by optimizing lipid metabolism during transition period management and early lactation. However, the RPC success in dairy cows depends on choline bioavailability, which is affected by the type of protection used in rumen-protected choline. Therefore, our objectives were to determine the effects of a novel RPC on dry matter intake (DMI), identify markers of metabolism and immunity, and evaluate lactation performance. Dry Holstein (n = 48) cows at 245 ± 3 d of gestation were blocked by parity and assigned to control or RPC treatment within each block. Cows enrolled in the RPC treatment received 15 g/d of CholiGEM (Kemin Industries, Cavriago RE, Italy) from 21 d prepartum and 30 g/d of CholiGEM from calving to 21 d postpartum. During the transition period, DMI was measured daily, and blood was sampled weekly for energy-related metabolites such as ß-hydroxybutyrate (BHB), glucose, and nonesterified fatty acids (NEFA), as well as immune function markers such as haptoglobin (Hp) and lipopolysaccharide-binding protein (LPB). Vaginal discharge samples were collected at the calving and 7 d postpartum and stored in microcentrifuge tubes at -80°C until 16S rRNA sequencing. The main responses of body condition score, body weight, DMI, milk yield, milk components, and immune function markers were analyzed using the GLIMMIX procedure of SAS with the effects of treatment, time, parity, and relevant covariates added to the models. The relative abundance of microbiome α-diversity was evaluated by 3 indexes (Chao1, Shannon, and Simpson) and ß-diversity by principal coordinate analysis and permutational multivariate ANOVA. We found no differences in DMI in the pre- and postpartum periods. Cows fed RPC increased the yields of energy- and 3.5% fat-corrected milk and fat yield in primiparous and multiparous cows, with an interaction between treatment and parity for these lactation variables. However, we found no differences in milk protein and lactose up to 150 DIM between treatments. Glucose, NEFA, and BHB had no differences between the treatments. However, RPC decreased BHB numerically (control = 1.07 ± 0.13 vs. RPC = 0.63 ± 0.13) in multiparous on the third week postpartum and tended to reduce the incidence of subclinical ketosis (12.7% vs. 4.2%). No effects for Hp and LPB were found in cows fed RPC. Chao1, Shannon, and Simpson indexes were lower at calving in the RPC treatment than in the Control. However, no differences were found 7 d later for Chao1, Shannon, and Simpson indexes. The vaginal discharge microbiome was altered in cows fed RPC at 7 d postpartum. Fusobacterium, a common pathogen associated with metritis, was reduced in cows fed RPC. Rumen-protected choline enhanced lactation performance and health and altered the vaginal discharge microbiome which is a potential proxy for uterine healthy in dairy cows. The current study's findings corroborate that RPC is a tool to support adaptation to lactation and shed light on opportunities for further research in reproductive health.

Effect of 200 µg of gonadorelin hydrochloride at the first GnRH of a CO-Synch program on ovulation rate and pregnancies per artificial insemination in Holstein heifers.

The initial ovulatory response during synchronization programs is often low in dairy heifers, largely due to follicular dynamics and hormonal dynamics. Specifically, the progesterone (P4) concentration at the time of the first GnRH treatment in a breeding program can influence the LH response, often resulting in a suboptimal ovulatory response. The objective of this study was to determine the effect of the highest label dose 200 µg (100 µg vs. 200 µg) of GnRH (50 µg of gonadorelin hydrochloride per mL; Factrel, Zoetis Inc. Madison, NJ) at the first GnRH of a 6-d CO-Synch plus P4 device program on ovulatory response and pregnancy per AI (P/AI) in first service in Holstein heifers. A total of 1,308 Holstein heifers were randomly allocated at the beginning of a 6-d CO-Synch program at day 0 to receive either i.m. treatment of 100 µg (2CC, n = 655) or 200 µg (4CC, n = 653) of GnRH. Also, at d 0, heifers received an intravaginal insert with 1.38 g of P4 (Eazi-Breed CIDR Cattle Insert, Zoetis Inc.). On day 6, the insert was removed, and i.m. treatment of 25 mg of PGF2α (12.5 mg of dinoprost tromethamine/mL; Lutalyse HighCon Injection, Zoetis Inc.) was administered. On d 7, a second i.m. treatment of 25 mg of PGF2α was given, followed on d 9 by concurrent i.m. treatment of 100 µg of GnRH, and timed AI. A subset of 396 heifers had their ovaries scanned to evaluate ovulatory response, and blood samples were collected to measure the serum concentration of P4 at d 0 and d 6 of the study. The P4 concentrations at d 0 were categorized as low (≤3 ng/mL) or high (>3 ng/mL). The ovulatory response was greater for heifers receiving 4CC than 2CC at d 0 (54.7% vs. 42.8%). The ovulatory response was greater for low P4 than high P4 at d 0 (54.3% vs. 37.8%). However, we did not observe an interaction between treatment and P4 concentrations (low P4 2CC = 48.6% vs. high P4 2CC = 30.0%; low P4 4CC = 60.0% vs. high P4 4CC = 45.5%). The receiver operating characteristic curve analysis indicated that P4 concentrations at d 0 treatment could predict the ovulatory response, although the area under the curve was only 0.6. As expected, heifers that ovulated had increased P/AI (no = 55.6% vs. yes = 67.7%); however, we found no effect of treatment on P/AI (2CC = 63.3% vs. 4CC = 59.6%), and no interactions between treatment and ovulation and treatment and P4 (high vs. low) for pregnancy outcomes. In summary, P4 concentration and increasing the dose of GnRH at d 0 positively affected ovulatory response in Holstein heifers. However, there was no interaction between treatment and P4 on ovulation and no subsequent impact of GnRH dose on P/AI.